Copper(I) Complexes, Copper(I)/O2Reactivity, and Copper(II) Complex Adducts, with a Series of Tetradentate Tripyridylalkylamine Tripodal Ligands

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Abstract
Copper(I) and copper(II) complexes possessing a series of related ligands with pyridyl-containing donors have been investigated. The ligands are tris(2-pyridylmethyl)amine (tmpa), bis[(2-pyridyl)methyl]-2-(2-pyridyl)ethylamine (pmea), bis[2-(2-pyridyl)ethyl]-(2-pyridyl)methylamine (pmap), and tris[2-(2-pyridyl)ethyl]amine (tepa). The crystal structures of the protonated ligand H(tepa)ClO4, the copper(I) complexes [Cu(pmea)]PF6 (1b-PF6), [Cu(pmap)]PF6 (1c-PF6), and copper(II) complexes [Cu(pmea)Cl]ClO4·H2O (2b-ClO4·H2O), [Cu(pmap)Cl]ClO4·H2O (2c-ClO4·H2O), [Cu(pmap)Cl]ClO4 (2c-ClO4), and [Cu(pmea)F]2(PF6)2 (3b-PF6) were determined. Crystal data: H(tepa)ClO4, formula C21H25ClN4O4, triclinic space group P1̄, Z = 2, a = 10.386(2) Å, b = 10.723(2) Å, c = 11.663(2) Å, α = 108.77(3)°, β = 113.81(3)°, γ = 90.39(3)°; 1b-PF6, formula C19H20CuF6N4P, orthorhombic space group Pbca, Z = 8, a = 14.413(3) Å, b = 16.043(3) Å, c = 18.288(4) Å, α = β = γ = 90°; (1c-PF6), formula C20H22CuF6N4P, orthorhombic space group Pbca, Z = 8, a = 13.306(3) Å, b = 16.936(3) Å, c = 19.163(4) Å, α = β = γ = 90°; 2b-ClO4·H2O, formula C19H22Cl2CuN4O5, triclinic space group P1̄, Z = 4, a = 11.967(2) Å, b = 12.445(3) Å, c = 15.668(3) Å, α = 84.65(3)°, β = 68.57(3)°, γ = 87.33(3)°; 2c-ClO4·H2O, formula C20H24Cl2CuN4O5, monoclinic space group P21/c, Z = 4, a = 11.2927(5) Å, b = 13.2389(4) Å, c = 15.0939(8) Å, α = γ = 90°, β = 97.397(2)°; 2c-ClO4, formula C20H22Cl2CuN4O4, monoclinic space group P21/c, Z = 4, a = 8.7682(4) Å, b = 18.4968(10) Å, c = 13.2575(8) Å, α = γ = 90°, β = 94.219(4)°; 3b-PF6, formula [C19H20CuF7N4P]2, monoclinic space group P21/n, Z = 2, a = 11.620(5) Å, b = 12.752(5) Å, c = 15.424(6) Å, α = γ = 90°, β = 109.56(3)°. The oxidation of the copper(I) complexes with dioxygen was studied. [Cu(tmpa)(CH3CN)]+ (1a) reacts with dioxygen to form a dinuclear peroxo complex that is stable at low temperatures. In contrast, only a very labile peroxo complex was observed spectroscopically when 1b was reacted with dioxygen at low temperatures using stopped-flow kinetic techniques. No dioxygen adduct was detected spectroscopically during the oxidation of 1c, and 1d was found to be unreactive toward dioxygen. Reaction of dioxygen with 1a-PF6, 1b-PF6, and 1c-PF6 at ambient temperatures leads to fluoride-bridged dinuclear copper(II) complexes as products. All copper(II) complexes were characterized by UV−vis, EPR, and electrochemical measurements. The results manifest the dramatic effects of ligand variations and particularly chelate ring size on structure and reactivity.